The present disclosure relates to a semiconductor laser device assembly.
Recently, an ultrashort pulse/ultrahigh output laser has been actively used for making a study of an advanced scientific domain using a laser beam where a pulse time width is at an atto-second level or a femtosecond level. In addition, in the ultrashort pulse laser, in addition to a scientific interest called the elucidation of ultrafast phenomena such as picoseconds and femtoseconds, an application study to practical use such as minute processing or two-photon imaging has been actively performed using high peak power. In addition, a high-output ultrashort-pulse semiconductor laser element that is configured from a GaN compound semiconductor and has a light emission wavelength in a 405 nm band has been expected as a light source of a volume-type optical disk system expected as a next-generation optical disk system following a Blu-ray optical disk system, a light source required in fields such as a medical field and a bio-imaging field, and a coherent light source covering an entire region of a visible light region.
As the ultrashort pulse/ultrahigh output laser, a titanium/sapphire laser has been known. However, the titanium/sapphire laser is expensive and is a large-scale solid-state laser light source, which results in becoming a main factor that disturbs a technical spread. In addition, a different solid-state laser to oscillate consecutive light is necessary for excitation and energy efficiency is not necessarily high. Besides, it is not easy for a large-scaled resonator to realize mechanical stability and specialized knowledge is required on maintenance. If the ultrashort pulse/ultrahigh output laser can be realized by a semiconductor laser element (LD), large downsizing, price reduction, low consumption power, and high stability are enabled, which results in a breakthrough on promoting the extensive spread in these fields.
Meanwhile, peak power of a light pulse can be represented by an average output/(repetition frequency×pulse width). Therefore, it is effective to increase the average output to realize the high peak power. In the related art, when an external resonator structure is configured by a diffraction grating, technology for returning first order diffraction light to a semiconductor laser element and extracting zero-th order diffraction light to the outside is known. Generally, in the diffraction grating, diffraction efficiency at a blaze wavelength is highest and diffraction efficiency of polarized light (for convenience, referred to as “parallel polarized light”) in which a vibration direction of a field in a laser beam (hereinafter, it may be simply referred to as the “field”) and rulings of the diffraction grating are parallel to each other is lower than diffraction efficiency in polarized light (for convenience, referred to as “orthogonal polarized light”) in which the vibration direction of the field and the rulings of the diffraction grating are orthogonal to each other. In addition, technology for making orthogonal polarized light incident on the diffraction grating and improving diffraction efficiency is known from JP 3-145174 A, for example.